A multi-core telecommunications cable may have many tens or hundreds of conductor pairs, and some means may be required for terminating such a cable for final connection to drop wires that lead to, for example, subscriber's telephones.
Various types of terminal blocks have been used for this purpose, each containing some means for anchoring an incoming multi-core cable and having a number of pairs of conductors, known as binding posts, to a base of each of which a conductor of the cable is more or less permanently connected. A top part of each binding post protrudes above an upper surface of the block, and is screw threaded. A stripped drop-wire may be wrapped around the exposed binding post and secured with a washer and nut, thus making a breakable-electrical connection between a core of the incoming cable and the drop-wire. A terminal block may typically provide for connections of up to 25 pairs of conductors, a pair of conductors of course being required for each telephone.
An improved terminal block is disclosed in U.S. Pat. application No. 70,475 filed 7 July 1987 (Shimirak, Huynh), the disclosure of which is incorporated herein by reference. That improved terminal block comprises:
an insulative housing containing a plurality of spaced-apart conductive binding posts;
conductive binding posts having opening means therein for receiving insulated wires; and
caps on the binding posts;
wherein:
the insulative housing has first opening means therein aligned with the opening means in the binding posts whereby an insulated wire is received through the opening in the housing and into the opening in the binding posts; and
the binding posts have thread means for engaging a threaded cap and have first shoulder means positioned between the threaded means and the opening means for engaging opposite shoulder means in the cap and have second shoulder means positioned on the opposite side of the opening means which second shoulder means is adapted for supporting the wire when pressure is applied to the wire by the cap threaded onto the binding posts; and the caps have a conductive inner portion and an insulative outer portion wherein the conductive inner portion has thread means adapted to engage the thread means on the binding posts and has shoulder means at the end of said thread means for engaging the first shoulder means of the binding posts and has bottom edge means for engaging the wire positioned in the opening means of the binding posts and compressing the wire against the second should means of the binding posts as the cap is tightened on the binding posts whereby the edge means contacts a conductor in the wire by passing through insulation on the wire;
wherein the distance between the shoulder means in the cap and the edge means of the cap is such that when the should means in the cap seats against the first shoulder means of the binding posts the distance between the edge means of the cap and the second shoulder means of the binding post is a preselected distance which allows connection of the edge means of the cap through the insulation of the wire to a conductor in the wire without breaking or severing the wire; and
wherein the housing has second opening means positioned substantially at right angles to said wire receiving openings through which second opening means the binding post extends and adapted for receiving the caps therethrough.
The binding posts and wire connected thereto may be sealed with a sealing material such as a gel, preferably having an ultimate elongation of at least 200%, and a cone penetration value of about 100 to about 350 (10.sup.-1 mm).
A further instance in which such a sealing material is used in conjunction with a termination block is disclosed in U.S. Pat. No. 4,600,261 (Debbaut), the disclosure of which is incorporated herein by reference. In that instance a gel is retained in one or more caps that are then positioned over binding posts, such that the gel is maintained under compression.
German Gebrauchsmuster G8514551 (Raychem) also discloses the use of such a gel to seal an electrical connection, but in this case a coaxial cable is sealed within a socket of a cable television (CATV) splitter box. The socket is provided with an expansion chamber or other means for accommodating gel that is displaced as the coaxial cable is pushed in place. The gel may automatically move back when the cable is withdrawn.
The situation in the case of a terminal block is rather different, since the proper positioning of a cap on a binding post may cause a sealing material to be driven out of the aperture through which a drop-wire enters. This may be messy, unsightly, and result in sufficient loss of gel that on subsequent use of the terminal in question a reliable seal is not achieved.